Pole barn truss spacing help

[shawnba67]

I am slowly building a pole barn type garage 24/48'. In southern Indiana My snow load is 15-30psf the truss spacing will be depentdant on the span the 1x4 oak barn wood I'm using as purlins can handle. Any experience or educated guess on how much span I might be able to get away with??
inspector says there's no applicable odes to concern myself with but I don't want it to be to weak to stay up Thanks much

[tja6435]

http://www.awc.org/codes-standards/calculators-software/spancalc

this calculates the span a piece of lumber can take, per your specs. It's very easy to use, I go to it to ensure I won't span too much or I buy the correct lumber for the span.

[Alstep]

30 psf snow load is pretty light. You get a foot of snow on your roof and it turns to rain, you've got one hell of a load. A cubic foot of water is 62 pounds. Maybe it's a rare occurrence in your area, but it only takes one time to collapse the barn. 1X4 is light for purlins, even if it's oak. If it's dry, oak is very hard to nail, splits easily, and you'll be twisting off screws when fastening your roofing. Be very selective of the knots. I wouldn't want to clime on them while building. We usually space trusses 4' OC with 2X4 purlins 2' apart. The steeper the roof, the more likely the show will slide off. You should also allow for an uneven load for snow slideoff and drifting. We get lots of snow here in upstate NY and never had a problem with those specs. Good luck with your project.

[Ickisrulz]

The truss builder should offer guidance on spacing.

[GOPHER SLAYER]

One of the accounts we served when I worked for the phone company was a very large carpeting distributer. The building warehouse was built using those wide wooden timbers made of layers wood glued together. I think they were 24 inches wide. It had been raining for days and everything was soaked. We got the call in the office to send repair crews to the address and when I arrived I couldn't believe my eyes. Those large timbers had broken under the weight of the rain which had collected on the roof. I asked if the drains for the roof had gotten plugged and they said no. The problem was the fact that the lot behind the building was full of water and the rain water had no place to go. The water had crashed thru the roof and flooded the hall ways, blew the doors off leading into office, swept thru the office and blew the doors and windows off the front of the building. The secretaries I talked to said it was the most terrifying thing they had ever lived thru. When I built a barn for my horse years later I remembered that event and I built the roof extra strong. The first winter after we built the barn we had a heavy snow storm. When we went down the feed the horse that morning there was several inches of snow on the barn roof.

[Plate plinker]

30 psf snow load is pretty light. You get a foot of snow on your roof and it turns to rain, you've got one hell of a load. A cubic foot of water is 62 pounds. Maybe it's a rare occurrence in your area, but it only takes one time to collapse the barn. 1X4 is light for purlins, even if it's oak. If it's dry, oak is very hard to nail, splits easily, and you'll be twisting off screws when fastening your roofing. Be very selective of the knots. I wouldn't want to clime on them while building. We usually space trusses 4' OC with 2X4 purlins 2' apart. The steeper the roof, the more likely the show will slide off. You should also allow for an uneven load for snow slideoff and drifting. We get lots of snow here in upstate NY and never had a problem with those specs. Good luck with your project.

Agree with this I do and I just built two pole barns here. 5/12 roof is what I like. Also, why mess with the oak for the roof purlins? Cheap? or some other reason? I would rather buy 2x4s and not worry about it the spacing and 2x4s are fairly straight and a lot easier to work with. My guess you will spend more money on trusses using those 1x4s than using 2x4 purlins at 2' spacing and 4'OC trusses. Trusses cost money.

[jonp]

http://www.awc.org/codes-standards/calculators-software/spancalc

this calculates the span a piece of lumber can take, per your specs. It's very easy to use, I go to it to ensure I won't span too much or I buy the correct lumber for the span.

Thats the one I use. I like the fact that you can use different wood species in figuring the load

[jonp]

I am slowly building a pole barn type garage 24/48'. In southern Indiana My snow load is 15-30psf the truss spacing will be depentdant on the span the 1x4 oak barn wood I'm using as purlins can handle. Any experience or educated guess on how much span I might be able to get away with??
inspector says there's no applicable odes to concern myself with but I don't want it to be to weak to stay up Thanks much

I wood double or even triple the snow load in figuring the trusses to account for an unseasonably heavy spring snow followed by rain. You have no idea how heavy that can be. I'm also wondering about the oak along with the others and the 1x4 being considered. I'm no expert but I wouldn't use that, I'd go at least 2x4.

[rl69]

What span are you rafters on? What pitch?

Most pole barns in this area or built out of 2 inch pipe on a 2/12 pich spanned at 20 feet with 6 inch c pearling's

the wood structures run a 2x12 beam with the post set a 16 feet . The rafters coming off of them normally on 2 foot centers with 2x4 pearling's on 2 foot centers

[bearcove]

Purlins need to be 2x4 set on edge use 50d pole barn nails we predrill the 2x4s. Get 20ft 2x4s and pick good ones the straighter they are the flatter your roof. and stagger the butts. 4 foot is plenty close this way. Some do 5 or 6 ft. My stuff is 4ft. Pitch doesn't matter if you have enough. You can stand on a 6/12 roof but not a 8/12. This is for Mo/Iowa border area.

Most metal roofs require this for the warranty.If you put up purlins flat the roof won't last. Lot of people don't read it.

[Plate plinker]

I seriously doubt those setups would pass in any part of Indiana due to snow. The metal maybe.

Referencing post #9

[MaryB]

When they built my new pole garage I had them spec the roof for 60 lbsf snow load + 2,000 pounds of solar panels... 2x6 purlins, trusses set 4' apart, poles on the gable ends 6' apart 6x6's... other walls were 8' oc poles.

[Lloyd Smale]

Building code in my county in Michigan is 70psf. I built mine at 90. I had to send back my pre made trusses that came with my pole barn package from menards. It was a mistake I made. I didn't know that menards packages are 60psf because there spec'd for Wisconson snow loads. Ended up what I though was the best price on a package ended up costing me more then if I would have bought it at the local building supply store. Found out when the building inspector came for his pre inspection and said no way! Best advice I to talk to your building inspector before you waste the time and money using the advice you get on here and keep in mind that whats code is whats MINIMUM.

[HABCAN]

Posts #10, #12 and #13............right on!! +1! Kanuckistan codes are even heavier, and specify MINIMUMS. It makes sense to 'outdo' your LOCAL code for lasting peace-of-mind.

[MaryB]

Other advantage of over building my roof is wind survival. I had them use hurricane tie down on the rafters and the engineer said my roof should be good to 140mph even with 16 solar panels mounted on it.

[Lloyd Smale]

yup mary people down south and people not in big snow country like up here have the wind to deal with. Good point.
Other advantage of over building my roof is wind survival. I had them use hurricane tie down on the rafters and the engineer said my roof should be good to 140mph even with 16 solar panels mounted on it.

[Teddy (punchie)]

As what was asked. I would double up the oak boards and offset the joints. Make sure crowns are up. Don't use any wood that is too knotty or bowed too bad. If you would happen to have a joint mid span then over lap 4 times the width, so in you case 12" each side of joint. Use nails screws have no shear strength. Screws to hold down only.

[Petrol & Powder]

Lot's of good advice here but lots of unanswered questions as well.

The OP hasn't decided on his truss spacing or pitch and stated he will make those decisions based on what the purlins can handle.....
Maybe I missed something but that sounds like he is coming at that problem from the wrong side. To me, the decision on the purlins would be the last part of that engineering and that choice would be dependent on my prior decisions about truss spacing and pitch. Am I missing something?


We also don't know what style of roofing he intends to use. Standard 5 rib panels with external fasteners OR standing seam panels with hidden fasteners ? They both handle snow loads well but that decision should factor into your purlin spacing. Also, if standing seam is used the width of the pan (distance between seams) affects its ability to handle snow loads.


I agree with the advice to over build. Building to handle the average snow load or the average wind speed is inviting disaster. Do it once and do it right.


If the OP is using prefab factory made trusses, the truss manufacturer can, and will, provide engineering specs for those trusses.
I understand wanting to design a roof system that is economical to build but strong doesn't have to equal super expensive. Adding just a couple of trusses in order to reduce truss spacing (on center measurement) will cost you the price of a few trusses but pay off with much higher strength. A steeper pitch will require more roofing material to cover the roof but pays off in both increased static load handling ability and the ability to shed snow.


So I think the OP needs to sit down with pencil, paper, calculator and design an entire roofing system first. Then you can make intelligent decisions.

[Plate plinker]

Good points on snow loads. Might I mention scraping snow off a roof really sucks. Don't be that guy.

[CLAYPOOL]

Around here you can buy trusses pre-made cheaper than you can build your self . Slope the **** out of it.

[MaryB]

I went standard 4:12 pitch, snow slides right off... I slammed the man door and walked around to check the garage door was down and found out how well it slides when the avalanche hit me on the head!

[44man]

I never bought trusses, made my own from 2X6 and 16" on center. My addition needed a 5-12 slope the match the peak of the 4-12 roof.
I don't like trusses. I worked part time at a lumber yard and built them. I got a spec sheet but always laid one up first to find angles were wrong and nail plates too small. I was the chief sawer of all parts. But the guys on the press had to have the right stuff. I told the guys to go bigger on plates and got bitched by the boss. When I did it his way they could not load the trusses on the truck without breaking so the guys were hammering new plates on.
One day the boss was wrong for trusses for a huge motel. I fixed it fast and got a 25 cent raise. I saved him thousands. I quit that day. It was a good day when I told him it was wrong, he turned white until I told him I fixed it. Only lost a few boards.

[44man]

Same as cast basement walls. Also a part time job to carry 45 and 90# forms to lower into the holes. Full of form oil. Cement truck came and started to pour. Boss said "more water." It was not flowing to the end. NOT! Water is death to concrete.
My brother in law bought a house he poured the basement with. Heavy rain load split the wall top to bottom and flooded his basement. They came and filled the crack with tar.
Maybe I am the boolit master but I know one hell of a lot. I have been around the block. Don't fool with a 4' spacing. Over build. I have done it all, master plumber and electric. Concrete and block. Even TV repair back then. I can plumb and wire. Make anything. Footings to walls. Mechanic, fix cars and small engines. I Graduated West Tech as an auto mechanic. Got into big trucks.
Snow load is not 4' spacing. The purloins need support. Put trusses closer.

[Skooterr]

Another vote for 2 ft on center, if snow is a concern. My son's, he built 2 yrs ago.

http://i232.photobucket.com/albums/ee95/dmystix/0614141607-00_zpsmqvej3n4.jpg (http://s232.photobucket.com/user/dmystix/media/0614141607-00_zpsmqvej3n4.jpg.html)

http://i232.photobucket.com/albums/ee95/dmystix/20161130_095610_zpsl6wkisln.jpg (http://s232.photobucket.com/user/dmystix/media/20161130_095610_zpsl6wkisln.jpg.html)

http://i232.photobucket.com/albums/ee95/dmystix/0614141249-00_zpsh3m4dzve.jpg (http://s232.photobucket.com/user/dmystix/media/0614141249-00_zpsh3m4dzve.jpg.html)

http://i232.photobucket.com/albums/ee95/dmystix/0805150959-01_zpsxtkqekoj.jpg (http://s232.photobucket.com/user/dmystix/media/0805150959-01_zpsxtkqekoj.jpg.html)

[popper]

Interesting that truss design has no tension member.

[jsizemore]

Interesting that truss design has no tension member.

scissor truss

[Plate plinker]

Triangles is our friends.

[MaryB]

my trusses are 4' on center(garage is 24' wide)... but the truss design sets the loading, these were special order.

http://i226.photobucket.com/albums/dd248/maryalanab/IMG_20151020_1321003491_zpsxpinide2.jpg

8" wall insulation, R50 attic, overhead door is R26, fully lined with steel.

http://i226.photobucket.com/albums/dd248/maryalanab/IMG_20151117_1539397531_zpsgkuoqhr8.jpg

[blackthorn]

When I had my shop built I made the mistake of putting the vehicle access doors in the side (like Mary's). Now every time it snows I have to shovel the doors clear because the snow slides off the roof and piles up in front of the doors. Huge pain in the ---!!! My shop is 30x40 and IT IS TOO SMALL!

[shdwlkr]

Well I have poured more concrete then most will see in several life times. first never go past 3 1/2" slump no matter how hard it is to move, second mix should be 3500-4000 pound mix, wall should be at least 8" and I like 10-12" with at least one matt of number 4 reinforcing in it. Oh and don't work with less than 2" slump concrete as it is not in its plastic state if it isn't at least 2" and not more than 3 1/2" How much concrete have I poured well at last count it was in the thousands of yards. I built 450 bridges, way to many to remember box culverts, highways way past 500 miles for 25 years you do the math
Trusses I like 2x6 or 2x8 top plate and never go past 24 inch spacing.
Yes I over build but it is so much easier to spend a little more up front then deal with issues later

[MaryB]

My overhead door is on the roof slope side. I had closed the door and walked around the corner to make sure the overhead was closed all the way(I was still getting it adjusted right). Reason I built that way is because the slope faces south for solar panels... and to the street which is south.


When I had my shop built I made the mistake of putting the vehicle access doors in the side (like Mary's). Now every time it snows I have to shovel the doors clear because the snow slides off the roof and piles up in front of the doors. Huge pain in the ---!!! My shop is 30x40 and IT IS TOO SMALL!

[frkelly74]

Get an engineered truss from a reputable manufacturer with good insurance. Most of the failures I have observed of trusses due to overloading were caused by the trusses coming apart under load. Either the gang nails came loose allowing the truss to collapse or they tip over due to insufficient cross bracing. The engineer will specify truss spacing and what is to be used as purlins and their spacing. They will also specify internal permanent bracing. Unless you have the experience and confidence to do your own design , don't wing it.

[Oyeboten]

What is the Roof Pitch?

[Plate plinker]

What is the Roof Pitch?
I do not believe it is decided yet.

[Petrol & Powder]

I don't mean to be rude to the OP but until he decides the pitch and other variables, he can't set the truss spacing.

I can see in the picture provided by MaryB that although the trusses are on 4' centers, the purlins appear to be 2x4s on edge, taking advantage of the greater strength in that orientation. Those trusses also appear to be rather substantial for that application. Clearly a lot of engineering and thought went into that.

Reducing the spacing between the trusses increases the cost of the trusses (more trusses required) but that cost may be offset by other factors such as smaller purlins or lighter trusses? Like I said earlier, you need to sit down with pencil, paper & calculator first. Strong doesn't have to be super expensive.

[popper]

scissor truss Standard truss has a horizontal tension member to keep the walls from being pushed outward. Like the flying buttresses on the Cathedrals in Europe. You want the load pushing down, not out. Scissor members have to depend on bending of the arms to provide tension.